Watercress

Copper tape around the rim of the tub is unusually effective here, and rinsing cut sprigs matters because small snails hide in the crowded stem bases.

Irregular ragged holes chewed out of the middle of leaves and along the edges - not the clean-edged cuts a caterpillar leaves. Seedlings that vanish overnight, or that are cut off at soil level with nothing left behind. Silvery dried slime trails across leaves, soil, pots, and paving in the morning: this is the giveaway that tells you it was mollusks rather than an insect. Chewed pits in ripe fruit, especially where it rests on the ground. Damage that shows up on the lowest, dampest leaves first and gets worse after rain or evening watering. Turn over a board, an upturned pot, or a clump of dense mulch during the day and look for the animals themselves sheltering in the cool underneath.

Hand-picking works and costs nothing: go out an hour after dark with a headlamp, drop what you find into soapy water, and repeat nightly for a week or two - persistence is what wins, not any single product. Shallow beer traps sunk to soil level catch them too, but need emptying and refilling daily to be worth anything. Iron-phosphate bait is the standard control and is far lower-risk around pets and wildlife than the old metaldehyde products, but it is not harmless: many formulations include EDTA, and a dog that eats a quantity of pellets can develop iron toxicosis. Scatter it thinly per the label, never in piles, and keep dogs off a baited bed. Clear fallen foliage and debris in autumn, where the eggs are laid. In a wet climate this is a population you manage each season rather than one you eradicate - and on most established plants light grazing is cosmetic and needs nothing at all.

Take away the daytime shelter first: lift boards and upturned pots, clear piles of debris, keep dense mulch pulled back from crowns and stems, and give crowded plantings enough airflow to dry out. Water in the morning rather than the evening so the surface is dry by the time they come out. Copper tape around containers and raised beds gives them a shock they will not cross, and it is the one barrier that reliably works. Get plants past the vulnerable stage quickly - start seedlings in pots and set them out at a decent size rather than direct-sowing into a cold wet bed, since most plants stop being worth defending once the leaves toughen. Leave the ground beetles, frogs, toads, and ground-feeding birds alone, because they eat mollusks all night for free and broad-spectrum slug pellets kill them too. Where thick-leaved or resistant varieties exist for what you are growing, they take far less damage.

Slugs and snails are nocturnal mollusks that rasp ragged holes in soft leaves, shear off seedlings at ground level, and chew into ripe fruit that touches the soil. They feed at night and in the early morning and spend the day hidden under boards, pots, dense mulch, leaf litter, and low foliage, becoming active in exactly the cool, damp, shaded conditions that suit young plants. Damage is heaviest in wet spells and on tender spring growth: a single wet week can erase a row of seedlings while an established, tough-leaved plant of the same species is barely marked. They lay clusters of small pearly eggs in damp soil and under debris, so a garden with plenty of cover carries a resident population year after year rather than being invaded from outside.

A hard rinse of the whole stand with clean water usually clears a colony, and cutting the crop back hard removes the rest.

Dense clusters of tiny insects packed onto shoot tips, flower buds, and the undersides of young leaves. Curled, cupped, or distorted new growth that never opens properly. A sticky shine on the leaves - and on whatever sits under the plant - that later goes black with sooty mold. Tiny white cast skins left behind where a colony has been feeding. Ants running steadily up and down the stems, which is often the first thing you notice. Mottled, streaked, or misshapen leaves that do not grow out can mean a virus the aphids brought with them rather than the feeding itself.

Knock the colonies off with a hard jet of water and repeat every few days - on most plants that alone ends it. Pinch out or prune off the worst-infested tips rather than treating the whole plant. If colonies keep rebuilding, spray insecticidal soap or horticultural oil directly onto the insects, covering leaf undersides, and repeat weekly until they are gone; treat early or late in the day, and never spray a wilted or heat-stressed plant. Avoid broad-spectrum insecticides - they kill the ladybugs, lacewings, and parasitic wasps that were about to solve the problem for you, and aphid numbers usually come back worse afterward. Anything you spray must be labeled for the plant you are treating; follow that label and observe its pre-harvest interval. On anything you eat, wash leaves, heads, and buds well before use, since aphids hide down in crowns, folds, and tight growth.

Go easy on nitrogen: the soft, lush growth that heavy feeding produces is exactly what aphids breed on. Check new growth once a week through spring and early summer so you catch colonies while they are still small, and rub the first few out with your fingers. Leave flowering plants nearby and skip broad-spectrum sprays - ladybugs, lacewings, hoverflies, and parasitic wasps do most of this work for free, and they only stay if there is something for them to eat. Keep ants off the plant where you can, since they protect aphids from those predators. Water steadily so plants are not stressed, and check any new plant over before you bring it home or move it indoors, since aphids usually arrive on something else.

Aphids are small soft-bodied sap-suckers - green, black, gray, pink, or waxy white, and mostly wingless - that gather in dense colonies on the tenderest new growth: shoot tips, buds, and the undersides of young leaves. They breed extremely fast in mild weather, so a few can become hundreds inside a week. Their feeding curls and distorts soft growth, and the sticky honeydew they excrete coats everything below and turns black with sooty mold. Ants often farm and defend the colonies for that honeydew. A few aphids are normal on almost any plant and a healthy plant shrugs them off; only dense, persistent colonies do real damage, and some aphids also spread plant viruses as they feed.

Most cases in home culture trace back to using pond or stream water.

Roots that are short, swollen, brown and bent rather than white and straight - lift a plant and look. Stunted growth and small leaves with yellow or reddish-purple tints, particularly in cool weather. A stand that stops regrowing after cutting. Symptoms spreading through a container from one area outward.

There is no home cure for an infected stand. Discard the affected plants and the water, scrub and dry the container, and start again from seed or from cuttings taken off a clean plant. Since the organism travels in water and debris, sanitation between crops is the whole control.

Use clean water from a mains or well source rather than pond, ditch or stream water, and do not reuse water from an affected container. Start with clean seed or cuttings from a healthy plant, not material from a wild stand or an ailing pot. Wash out containers and trays between crops. Keep water moving and refreshed rather than stagnant, and avoid crowding.

The characteristic disease of watercress grown in standing or recirculating water, caused by the soil-borne organism Spongospora subterranea f. sp. nasturtii, which also carries a virus that worsens the symptoms. It infects the roots, which swell, twist and turn crooked and brown instead of running white and straight, so the plant cannot take up water and nutrients properly. Growth stalls, leaves yellow and redden, and stands thin out. It is favored by cool water, which is why it is mainly a winter and early-spring problem, and it persists in contaminated water, containers and old plant material.

A fine mesh cover over the container from sowing is the practical answer, and it also keeps cabbage whites off; damage is worst on a container sitting in a warm dry spot, which is the wrong place for watercress anyway.

Dozens of pinhead-sized round holes peppered across the leaves, thickest on the youngest, most tender growth. Tiny beetles that spring away as you brush the plants or lean in for a closer look - that jump is the identification. Seedlings that go lacy and stop growing, and transplants that sit and sulk instead of taking off. Damage heaviest in warm, dry weather and along the edge of a bed nearest weedy ground or last year's crop debris. On root crops, shallow narrow grooves or channels scarring the skin at harvest, from larvae feeding underground.

Row cover and healthy fast growth carry most crops through, and on an established plant the damage is usually cosmetic and needs nothing at all. Where a young planting is genuinely being stripped, kaolin clay coats the leaves and deters feeding, and spinosad will knock the beetles back. Spinosad is acutely toxic to bees while the spray is still wet - apply it at dusk when bees are not flying, never onto plants in flower, and follow the product label. Anything you spray must be labeled for the plant you are treating, and you must observe its pre-harvest interval on a crop you are picking. Yellow sticky traps are useful for telling you when the beetles have arrived. Where the damage falls on the part you eat, harvesting young often beats them outright; where you are growing for a root or a fruit, leaf damage can simply be tolerated. Larvae feeding underground cannot be reached by a foliar spray, so rotation and clean beds are what work against those.

Floating row cover or fine insect mesh, laid over the bed from the day of sowing or transplanting and sealed at the edges so nothing can walk in underneath, is the single best defense - and on the crops they favor it is close to essential. Leave it on until plants are large and growing strongly, or until flowering on anything that needs pollinating. Push growth: a well-watered, unchecked plant outgrows the damage, so the whole game is getting seedlings through their vulnerable weeks fast. Keep beds weed-free, since related weeds host the beetles alongside your crop, and clear crop debris at the end of the season where the adults overwinter. Rotate away from a bed that grew a related crop last year. Where you can, shift sowing dates - cooler-season and fall plantings often miss the peak of adult feeding entirely.

Flea beetles are tiny dark beetles - often shiny black or bronze, rarely more than a couple of millimeters long - with enlarged back legs that let them spring away like fleas the moment you lean in. The adults chew countless small round pits and shot-holes through leaves, giving the foliage a peppered, buckshot-riddled look. They overwinter as adults in leaf litter, hedgerows, and crop debris, emerge hungry in spring, and are worst in warm dry spells. The damage is mostly a seedling and transplant problem: a small plant with a few leaves can be checked, stunted, or killed outright, while the same plant shrugs them off once it is large and growing strongly. Different species specialize on different plant families, so the beetles hammering your brassicas are not the ones on your nightshades. Some species also have larvae that feed on roots and tubers underground.